hearth brick

[Avasquez]

Hello oven builders of the world do I use split brick for the hearth if not what thickness do they need to be. Also do I need a vapor barrier under the fb insulation that sits on the concrete slab that I poured the slab 3 months ago?
thank you, Adrian

[gastagg]

I think that the brick thickness is up to you. I think that the kits from FB come with larger pieces that are 1/2 the thickness of bricks. I used full bricks, and I think most guys do. As far as vapor barrier under the insulation, that would keep it from drawing any moisture from the slab if it gets wet. Some guys recommend it for certain. Not everyone does. Jump on a couple of full-build threads to see what they did and more than likely you'll run into some very experienced and helpful people with 1000+ posts and quite a bit of experience in building ovens. Send them direct messages and I'm sure you'll get very helpful advice fairly quick. If you keep the posts coming, esp. with pics, you'll get the help you need.

[RandyJ]

If you are building with fire bricks then you want the full 2.5" thick bricks. Otherwise you won't have enough thermal mass to cook several pizzas in a row. And forget about extended baking. As for the vapor barrier you would put that between the slab and insulation.

Randy

[Avasquez]

Ok thanks everyone, a full brick it is.

[Alomran]

If you are building with fire bricks then you want the full 2.5" thick bricks. Otherwise you won't have enough thermal mass to cook several pizzas in a row. And forget about extended baking. As for the vapor barrier you would put that between the slab and insulation.

Randy

I am not sure you need a vapour barrier for any oven as the heat generated in one burn would eliminate any dampness for weeks to come.

[david s]

I am not sure you need a vapour barrier for any oven as the heat generated in one burn would eliminate any dampness for weeks to come.

No, that's not correct. Many oven owners report the performance of their ovens takes quite a long time and many burns to improve. Eliminating the water beneath the oven floor, particularly if you use vermicrete does not happen quickly.
The main purpose of the vapour barrier between the insulation and the supporting slab is to prevent rising damp entering the porous floor insulation and floor bricks. While it's not essential it may be useful depending on your climate, oven situation, nearby irrigation etc.

[jonv]

Seeing just how much and how quickly calsil soaks up moisture, I'm glad I took the advice to waterproof the top of my slab.